Radio frequency (RF) transceivers may use quadrature modulation for higher spectral efficiency. The quadrature signals that are used for modulation and demodulation directly affect the performance of the transceiver and thus it is desirable that the quadrature signals be precise and have a low phase noise. Consequently, these signals may be generated locally at the transceiver.
In some conventional transceivers, an oscillator is used to produce an initial frequency at four times the desired frequency of the quadrature signals. The initial frequency is then divided down using at least two stages of digital dividers.
It is well known that generating a high frequency signal may be difficult due to device parasitic capacitances and inductances in the process. This, and the fact the in some conventional transceivers, the source oscillator oscillates at a frequency four times higher than the desired frequency of the quadrature signals, currently limit the quadrature signal frequencies that can be generated. High frequency signals also tend to have a high phase noise.
It is also known that digital dividers are high bandwidth devices, and consequently, the quadrature signals at their output may have more phase noise than the original signal before division.